1. Technical Field
The present invention relates to telemonitoring systems for digital signal repeaters sequentially disposed along a data transmission line.
2. Discussion of the Prior Art
The use of data transmission lines for transmitting coded digital signal, and particularly data transmission lines employing a sequence of interposed signal repeaters, is well known in the prior art. In view of the importance of transmission accuracy, repeater telemonitoring must be employed and must possess a high degree of effectiveness, rapidity, flexibility, standardization and economy. There are many telemonitoring systems in use, and among them is a relatively recent system which provides for the forward transmission of an interrogation signal from a remote terminal to a repeater which answers with a status information signal that is transmitted toward the next repeater. When there is no interrogation signal, the repeater itself forwards the interrogation signal to the following repeaters, although no telemonitoring signal is forwarded when a check of the information quality fails. The information quality test of the repeaters yields information about only a few specific repeater parameters, namely: faulty repeater; degraded repeater operation; and normally operating repeater. There are numerous disadvantages inherent in such a system. For example, for the telemetry signal of the transmitter in a first terminal (e.g., a remote terminal), the system requires the interrogation signal plus a signal which detects answers in a second terminal (e.g., a next terminal). Further, although a remote transmitter is of itself simple, it must be duly protected at the time of telemetry failures or else it can pollute the telemonitoring signal and thereby prevent automatic reading of telemetry circuit failures. In addition, the number of repeaters which can be meaningfully monitored with such a system is defined by the alternation of the interrogation signals. Still further, the information concerning repeater status represents only three parameters, namely fault, normal operation and degraded operation. In such a system it is not possible to detect either micro-failures (e.g., on-line bursts) or error storage (e.g., error accumulation). A further disadvantage is that the technology has become obsolete and therefore does not permit reduction in either cost and power consumption. Finally, the aforesaid prior art system results in different or non-standard construction of a terminal when the terminal must act as a buffer to the telemetry signal.